Problem: Complete the recursive formula of the geometric sequence $56\,,-28\,,\,14\,,-7,...$. $d(1)=$
Explanation: The first term is $56$ and the common ratio is $-\dfrac12$. ${\times\left(-\dfrac12\right)\,\curvearrowright}$ ${\times\left(-\dfrac12\right)\,\curvearrowright}$ ${\times\left(-\dfrac12\right)\,\curvearrowright}$ $56,$ $-28,$ $14,$ $-7,...$ This is the recursive formula of $56\,,-28\,,\,14\,,-7,...$. $\begin{cases} d(1)=56 \\\\ d(n)=d(n-1)\cdot\left(-\dfrac12\right) \end{cases}$